[dm-devel] trim support (discard)

[Jens Kasten]

Am Sonntag, den 09.01.2011, 14:28 +0100 schrieb Milan Broz:
> On 01/08/2011 08:45 PM, Jens Kasten wrote:
> > 
> > I use the kernel 2.6.37 with cryptsetup and lvm on a intel ssd. 
> 
> Device-mapper targets supports discards in 2.6.37 with exception
> of dm-crypt target (that's why you see that message).
> 
> Supporting discards in dm-crypt means that information
> about unused blocks is leaked (SSD ususally returns zeroes instead
> of expected random data for discarded blocks) and it it can be
> security problem in some situations.

Thank you, for this information.
About this i have never thought.
   
> We will probably add discard support in dm-crypt later but as optional
> parameter (admin must decide that leaking allocated block info
> is not problem and must explicitly enable it).
> Probably 2.6.39 material.
> 
> > Then i try the wiper.sh script and i get:
> > wiper.sh: Linux SATA SSD TRIM utility, version 3.1, by Mark Lord.
> > /dev/dm-1: unable to reliably determine the underlying physical device
> > name, aborting

Ok, I take a look on the script.

> That seems like bug in that script btw, it should understand DM devices.
> 
> > Its there in near future the discard support on the LVM?
> 
> LVM/DM itself should fully support discards now.
> Exception is stacking with dm-crypt devices.
> 
> Milan
> 
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